The present invention relates to a fuel electrode for high-temperature solid electrolyte fuel cells and a method for manufacture of the electrode.
Heretofore, nickel/zirconia (Ni/ZrO.sub.2) cermets have been employed for fuel electrodes in commercialized high-temperature solid electrolyte fuel cells.
These Ni/ZrO.sub.2 cermets are typically produced by the following alternative processes.
(1) A process in which NiO/ZrO.sub.2 is sintered and then reduced to provide a Ni/ZrO.sub.2 cermet (e.g. the Ceramatec process described in Proceedings of SOFC-NAGOYA, p.24). PA1 (2) A process, known as Westinghouse process, in which ZrO.sub.2 in a crude Ni/ZrO.sub.2 cermet is caused to grow into spaces between Ni grains by the EVD technique (Japanese Kokai Patent Publication No. 61-153280). PA1 (1) A high melting point and stability even in a reducing atmosphere; PA1 (2) Low cost; and PA1 (3) High catalyst activity for steam reforming of CH.sub.4 which is an important factor in electrode performance. PA1 (1) Substantially no sintering occurs even when the fuel cell is run for thousands of hours at 1,000.degree. C. PA1 (2) Each of the reaction, diffusion and resistance polarization values are as small as several mV at 200 mA/cm.sup.2.
Aside from the above, porous platinum (Pt) materials obtainable by sintering platinum pastes have been used in ZrO.sub.2 sensors and the like or in basic research.
However, the Ni/ZrO.sub.2 cermet electrode manufactured by the first-mentioned process is disadvantageous in that when the fuel cell is run over thousands of hours at temperatures near 1,000.degree. C., the Ni grains therein are sintered to degrade the electrode and ultimately cause exfoliation of the electrode. Increasing the proportion of ZrO.sub.2 for avoiding this sintering detracts from the performance of the electrode.
The Ni/ZrO.sub.2 cermet manufactured by the second-mentioned process is resistant to sintering and insures a satisfactory electrode performance, but, since it involves an EVD step, the overall manufacturing process is complicated and the cost of manufacture is increased.
The porous platinum electrode is disadvantageous in that the platinum reacts with the impurity metal in the fuel and is vaporized in continuous operation in a reducing atmosphere resulting in early aging of the electrode. Furthermore, platinum is an expensive metal and the manufacture of porous platinum electrodes is costly.